1. Field
The present disclosure relates generally to communication, and more specifically for scheduling in a wireless communication network.
2. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-input-single-output (SISO), multiple-input-single-output (MISO), single-input-multiple-output (SIMO) or a multiple-input-multiple-output (MIMO) system.
Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) cell phone technologies. UTRAN, short for UMTS Terrestrial Radio Access Network, is a collective term for the base nodes (Node B's) and Radio Network Controllers (RNC) which make up the UMTS core network. This communications network can carry many traffic types, from real-time Circuit Switched to IP based Packet Switched. The UTRAN allows connectivity between the UE (user equipment) and the core network. The UTRAN contains the base stations, which are called Node Bs, and RNCs. The RNC provides control functionalities for one or more Node Bs. A Node B and an RNC can be the same device, although typical implementations have a separate RNC located in a central office serving multiple Node B's. Despite the fact that they do not have to be physically separated, there is a logical interface between them known as the Iub. The RNC and its corresponding Node Bs are called the Radio Network Subsystem (RNS). There can be more than one RNS present in an UTRAN.
Third Generation Partnership Project (3GPP) LTE (Long Term Evolution) is the name given to a project within the 3GPP to improve the UMTS mobile phone standard to cope with future requirements. Goals include improving efficiency, lowering costs, improving services, making use of a new spectrum of opportunities, and better integration with other open standards. The LTE system is described in the Evolved UTRA (EUTRA) and Evolved UTRAN (EUTRAN) series of specifications. In order to provide improved communication services and increased efficiency, cellular communication systems are continuously developed and enhanced. Currently, the 3rd Generation Partnership Project (3GPP) standards body is in the process of standardizing improvements to the Universal Mobile Telecommunication System (UMTS) known as LTE.
Similarly, to advanced communication services, such as High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), LTE uses a very fast scheduling of communication resources allocated to user traffic and control data over the air interface. Specifically, scheduling for user traffic may be performed in the individual serving base station (eNodeB) thereby allowing scheduling to be so fast that it can follow changes in the characteristics of the propagation channels to the individual User Equipments (UEs). This is used to schedule data for UEs such that data is predominantly scheduled for UEs which currently experience advantageous propagation conditions. The fast scheduling may be performed both for uplink user data traffic transmitted on a physical channel known as the Physical Uplink Shared CHannel (PUSCH) and for downlink user data traffic transmitted on a physical channel known as the Physical Downlink Shared CHannel (PDSCH).
In LTE, the resource allocation can be changed in sub-frames having a duration of only 1 ms with a typical scheduling interval (i.e., how often the scheduling algorithm runs) of between 1 and 10 sub-frames. One frame consists of 10 such consecutive sub-frames. The PUSCH and PDSCH are shared channels wherein the scheduling is not only dependent on the current propagation conditions but also on the resource requirement of the UEs. In order to simplify the scheduling and to reduce the signaling overhead, LTE allows for persistent scheduling wherein a resource allocation for the PUSCH or PDSCH may be made for a plurality of subframes.
In order to provide efficient fast scheduling in the base station, the UE must transmit uplink control information to the scheduling base station. Specifically, the UE transmits Channel Quality Indicator (CQI) data which is indicative of the current propagation conditions for the UE. Based on the measurements of the received signal, the UE generates a CQI which may indicate a modulation scheme and data rate that is considered to be supportable by the air interface communication channel from the base station to the UE, or which may be a measure of the Signal to Noise plus Interference Ratio. As another example, LTE uses a retransmission scheme (referred to as Automatic Repeat reQuest (ARQ) or Hybrid ARQ (HARQ)) and the UE transmits ARQ data in the form of uplink acknowledge (ACK) or non-acknowledge (NACK) messages which are used to determine whether individual data packets need to be retransmitted. As yet another example, LTE allows the base station to utilize adaptive antenna technology and the UE may report a Precoding Matrix Index (PMI) which is used to signal the antenna weights recommended by the UE for the individual antenna elements.
The uplink control information is transmitted using physical uplink channels. Specifically, in sub-frames wherein the UE transmits uplink user data traffic on the PUSCH, the control data is embedded within the transmission such that the control information is transmitted to the base station using the PUSCH. However, for sub-frames wherein no uplink user data traffic is transmitted on the PUSCH, the UE uses a physical uplink channel known as the Physical Uplink Control CHannel (PUCCH) to transmit the control information. Thus, the physical air interface channel used for the transmission of the control information may change for different sub-frames.